The present invention relates generally to group III-arsenide binary or ternary compound semiconductor substrates and devices and more specifically to contact for these devices.
Semiconductor devices made with group III-arsenide alloys, for example gallium arsenide, have increased in their use. Presently ohmic contacts to gallium arsenide substrates or devices use a gold-germanium alloyed contact. These contacts start to degrade in an unpredictable manner when processing temperatures exceed 400.degree. centigrade. Alloying also produces pitted metal/GaAs interfaces which can give rise to high field regions, current crowding with associated local joule heating, enhanced electromigration, and eventual device failure. This places a substantial restriction on the final processing steps, including packaging and die attachment.
Thus it is an object of the present invention to provide an ohmic contact structure to group III-arsenide substrates which does not restrict the final processing and packaging temperatures.
These and other objects are obtained by using polycrystalline silicon as the contact to regions of a group III-arsenide substrate. The substrate may be gallium arsenide or other group III-arsenide compound semiconductor. A heavily doped N type contact region is formed in the N type substrate region by heating the device sufficiently to out-diffuse silicon impurities from the polycrystalline silicon contact into the N type region. The N type region may be sources or drains of field effect transistors. The process of formation includes forming an opening in an insulative material, which may be silicon nitride, silicon dioxide or tantalum oxide and applying the polycrystalline silicon contact material into the opening. The heating of the substrate will diffuse silicon from the contact material into the substrate to form the heavily doped N type contact region.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.